The present invention relates to an arrangement for the fastening of cutting inserts for the chip forming machining of metals.
Different cutting inserts and indexable inserts are fastened on tool holders in several different known ways. One of the most common is that the insert has a central through hole and the insert pocket in the holder has a threaded hole. A locking screw is inserted through the central hole of the insert and is screwed into the hole in the holder with a suitable torque. A shim with a center hole is often placed between the insert and the bottom support surface. Usually, the insert pocket also comprises two internal, substantially perpendicular abutment surfaces, or three abutment points, for abutting against two of the insert's side surfaces. The disadvantage with this design is that a certain amount of play can easily occur after a period of use. A further drawback is that the screw can easily be tightened excessively, thereby damaging the screw or causing it to break.
Other known insert holders have a clamp or similar fastening arrangement, which presses upon the upper surface of the insert in order to clamp it in the insert pocket. The clamping force can be regulated by a screw. Such designs may, for instance, be used to fasten cutting inserts which have no center hole, which is the case for, among others, grooving and parting inserts.
In order to avoid play and in general to attain a more stable fastening of a cutting insert, designs have been suggested according to which the lower surface of the cutting insert and the bottom support surface of the insert pocket have been formed as ribbed surfaces which are intended to match each other. Such designs are disclosed in U.S. Pat. Nos. 2,140,941 and 2,453,464. However, a drawback with these embodiments is that they necessitate a considerable amount of grinding of the ribbed surfaces of either the cutting insert or tool holder, or both. A further drawback is that, even if the insert has been secured in a direction perpendicular to the ribs by means of a stop face behind the insert, a vertical play can occur just as easily with these designs as with those with two completely planar abutment surfaces, particularly in machining operations with a tendency to vibration.
In addition, there are a number of disadvantages associated with the use of a stop surface for the insert behind said insert. For example, it is only possible to mount inserts which are precisely suited to the length in question. In addition the shape of such a stop surface must be adapted to the geometry of the insert. The stop surface must not, for example, damage the non-active cutting edge which faces away from the workpiece. Furthermore such a stop surface can, to a certain extent, limit the accessibility of the insert and holder to the workpiece.
A system for clamping inserts on a holder is described in WO-A-95/29026, which is so arranged that it includes parallel grooves on the underside of the insert and ribs on the holder, whereby the ribs fit into the grooves. The insert is screwed fast in the holder, whereby a wedge action is created between the ribs and grooves. This wedge action and the friction between the flank surfaces of the ribs and grooves stabilize the insert to a significant degree in a radial direction (i.e., along a longitudinal axis of the holder which is oriented perpendicular to an axis of rotation of a workpiece), but when cutting forces are large this clamping action is not entirely reliable, and for this reason a rear stop surface must be utilized on occasions.
Thus a primary object of the present invention is to design a clamping system comprising an insert and a holder so that the use of a rear stop surface can be avoided.
A secondary object of the present invention is to design a clamping system in such a way that, the same holder can receive several inserts with different basic geometries.
A third object of the invention is to optimize the accessibility of the insert and holder with regard to the workpiece.
A further object of the invention is to design a clamping system which can in an optimal manner absorb both radial and axial cutting forces.